1. Field of the Invention
The present invention relates to polyether type non-porous polyurethane polymers excellent in moisture permeability, degree of swelling, and toughness and more particularly to polyurethane polymers which are useful for applications in a form of film and coating film.
2. Prior Art
In the past, materials which allow vaporized water, such as moisture, to permeate but do not allow the liquid water, such as rainwater, to permeate have been strongly sought after commercially. Products available in accordance with such demands are those, which utilize microporosity in which films are made microporous by stretching high crystalline tetrafluororesin and microporosity of urethane films made by a wet process. Non-porous films made of amino acid resins which utilize hydrophilic permeability, etc. are also available
As a method to provide polyurethane polymers which are a hydrophilic, it is well known that block copolymers of polyoxypropylene and polyoxyethylene or polyoxyethylene glycol may be used as a polyol component. It is also widely known that polyurethane hydrogel, which has the ability to absorb water several times over its weight, can be obtained by causing isocyanate terminal prepolymers, which are obtained from polyoxyethylene glycol of 4000 to 25,000 molecular weight and organic diisocyanate, to lightly cross-link with an equivalent amount of water or organic polyamine. (Japanese Laid-Open [Kokai] Patent Application No. 1976-13891).
Conventional microporous films have had some defects. Particularly, moisture permeability becomes lower when stains accumulate thereon; water pressure resistance decreases when the film is stretched, and the strength or toughness of the film itself is relatively low. Also, conventional non-porous films are defective in that some of them do not have sufficient moisture permeability, some of them are inferior in a long-term water-resistance since they have a high swelling ratio, and some of them are low in modulus of elasticity. Thus, they do not have appropriate physical properties to be used as films.
In addition, the moisture permeability of the non-porous film is almost reversely proportional to the thickness of the film. As a result, in order to obtain high moisture permeability, it is necessary to reduce the thickness of the film. For implementing thin films, the films must have appropriate modulus of elasticity (modulus).